Daugherty is right. 4w per gallon is a minimum for soft corals such as mushrooms and zoas. Most LPS will do okay under 4w per gallon - and many don't like super bright lights at all.
SPS, clams and anenomes require the most light. I'd shoot for 6w per gallon at a MINIMUM is thats the type of corals you plan to keep. 7w or 8w per gallon would be better IMHO.
But if you put 7w per gallon over mushrooms, LPS and zoas - they'll just bleach out and die. So you kinda have to decide what kind of tank you're going to build. You want a low light tank full of shrooms, polyps and LPS? Or you want a high light tank with SPS, clams and anenomes? It is possible to do all corals in a bright tank, but NOT the other way around. You can't do SPS, clams and anenomes in a low light tank. They'll slowly die.
If you decide to go for big light value, I don't think you'll ever be happy with the colors you see in your zoas, mushrooms LPS and other low light corals. You can keep them alive, but they won't be as colorful under such intense lighting. I know this from personal experience. I used to have a 10g frag tank with 78w of PC lighting. Thats 7.8w per gallon of PC lights. Most people poo-poo PC lights as under powered and a waste of money. I'll tell ya what, I watched all my zoas and mushrooms bleach out to pale brown colors under that kind of PC lighting. And thats with only (2) 10k bulbs and the other (4) bulbs were either actinic or 460nm (purple!). Those lights should have given me the most beautiful colors in the world, but it was SOOOO bright in there the corals bleached anyway. I ended up using my frag racks to shade corals and actually took out the 10k bulbs for a long time. Noticed a HUGE improvement in colors after just a month or maybe 6 weeks when I reduced the light.
I guess what I'm getting at -- it is possible to have too much light on certain types of corals. I've decided not to fight mother nature. I run low to medium light tanks and I keep LPS, mushrooms and zoas. Yote is the SPS expert - and yes, you DO need sunglasses and SPF 30 to view his tank. :mrgreen:
If I was you, I'd pick one now and run in that direction. It's very difficult to keep a mixed tank under just one type of lights - it'll always be too bright for some corals and not bright enough for your anenome and clams. My personal opinion is anenomes are tank killers and I'll NEVER have one. My clown can host in the palythoa polyps or in a clay pot. He's dumb as a box of cracker jacks anyway.
If that anenome in your tank ever gets "restless" and decides to go on walkabout in your tank - you can kiss all the rest of your corals g'bye. Ask Yote about that one. I think he had an anenome that walked around and killed a few thousand $$$ worth of SPS corals one time.